I've been on some sort of odyssey in the past week. There were many bumps, double posts, and posting on strange forums, but I might have found something. I've been having this issue for over a week, and I think I've finally narrowed it down to Steam somehow being the problem. Every couple seconds, I get a stutter. Framerate will drop from 60 or 300 (uncapped Source games) all the way down to less than 30, just for half a second, but enough for me to notice it and disrupt how smoothly the game plays. I tested it with Assassin's Creed II, Batman Arkham City, Half-Life 2, and Team Fortress 2. All of them had stutters/ framerate drops. I've already deleted the Steam folder, completely reinstalled it and reinstalled a couple games, but the problem is clearly persisting. It happens regardless of the video driver being used (currently using the most recent). I tried Mirror's Edge installed from a disc, no problem. Mass Effect 3 installed through Origin, no problems either. Add Steam shortcuts to those two games, run them through Steam, same problem as the Steam games. I disabled overlay, which is not an acceptable solution, but it doesn't matter because it did nothing to stop the problem in TF2 or HL2. So, all I can see is that Steam is somehow causing the issue. You might want to say it's a GPU bottleneck issue. Except this computer has had no bottlenecking issues at all in the past 6 months. This is only a recent problem, the past two weeks at most, and GPU and CPU temperatures are normal (30-40C idle, 60C under games). Again: Only in games run through Steam, and I've updated/ rolled back video drivers, makes no difference. Games not run through Steam, even Origin which has its own resource-sucking properties and its own overlay, are completely fine.